1. Field of the Invention
This invention relates to ophthalmology and more particularly to cataract extraction.
2. Description of the Prior Art
The natural lens of the eye is a lenticular-shaped body consisting of three readily distinguishable portions. The core portion is the nucleus and has the consistency of wax. Surrounding the nucleus is the cortex, a firm gelatinous material. Enclosing the cortex and constituting the wall of the lens is the capsule. "Cataract" is a medical term indicating either a degenerating or degenerated lens of the eye, or a localized point of degeneration within the lens. Cataractous degeneration results in opacification of the lens in varying degrees. As used herein, the term "cataract" is meant to imply a lens that has undergone cataractous change to an extent that the eye is visually significantly disabled.
Surgical procedures for dealing with cataracts have evolved over many centuries. Early techniques involved "couching", in which a blunt needle was inserted into the eye and used to push the lens out of the visual pathway. In the middle of the 18th century Daviel, a Frenchman, for the first time treated a cataract by removing it through an incision in the globe.
Since Daviel's time, two methods for extraction of a cataract have evolved. One is intracapsular extraction, the second, extracapsular extraction. When the cataract is removed without breaking the capsule, in other words, the lens in its entirety is removed, an intracapsular extraction is said to have been performed. By contrast, when the forward facing (anterior) portion of the capsule is removed followed by separate removal of the lens contents, an extracapsular extraction is performed. Generally, in an extracapsular extraction, the back (posterior) portion of the lens capsule is allowed to remain in the eye.
In the past 5 or 10 years, a strong trend has developed toward utilizing extracapsular technique in cataract extraction. Among other advantages felt to obtain through its use is the increased stabilization of the internal contents of the eye by virtue of retention of the posterior capsule.
In extracapsular cataract extraction, an incision is made into the eye, the anterior capsule is removed, then the nucleus is removed, following which the cortical remnants are extracted. Historically, the size of the nucleus has dictated the size of the incision which must be made for the cataract to be extracted. Since the nucleus may be as large in diameter as 10 or 10.5 mm, an incision of 10.5 to 12 mm is most commonly employed in this technique.
However, a smaller incision would present many advantages with respect to reducing operative time, increasing post-operative wound strength, hastening healing, and reducing the frequency of bleeding and infection complications. Therefore, attention has historically been given to the possibility of removing the nucleus through a smaller incision. Several years ago, a device called a phacoemulsifier was invented which allows the nucleus to be pulverized by high frequency vibrations and then aspirated. Using phacoemulsification, the lens can be removed through a 3 to 3.5 mm incision. Unfortunately, the phacoemulsifier presents potential for damaging the internal surfaces of the eye. Thus, though phacoemulsification apparatus is widely available in this country (despite its great expense), it is used in only perhaps 5% or less of cataract procedures.